The present invetion relates to an infrared camouflage system.
Infrared or IR detection of thermally dissipating equipment on the ground, when viewed against a cluttered background, depends upon the equipment contrast temperature, defined as an effective apparent temperature difference between the equipment and adjacent background surfaces. Usually, the contrast temperature difference must be limited to the background clutter limits, which are about 4 or 5 degrees C duing the day and about 2.degree. C. during the night. This must be done in such a way that these limits are maintained against any background such as, for example, soil, grass, trees, etc., and at all atmospheric conditions, including solar heating, wind cooling and intermittent cloud passage.
The thermal concealment requirement of meeting the aforestated clutter limits is difficult to meet in most instances, because apparent temperatures of different backgrounds differ from each other by as much as 20.degree. C. or more due to such factor as ground moisture and transpiration from vegetation. Additionally, constrast temperature is significantly affected by transient enviromental effects such as variable solar radiation, cloud patterns, wind and time of year. The key problem is the difference between the transient thermal responses of targets and backgrounds. Unlike the man-made camoflaged targets, the backgrounds have comparatively high thermal time constants and, therefore, respond relatively slowly to the changes in enviromental conditions.
Traditional attempts to cope with the stated thermal concealment difficulties are largely based on a passive thermal camouflage approach. This usually involves altering target camouflage and camouflage netting characteristics to match the target apparent temperature as closely as possible to one or several similar backgrounds. Typically, this done by tailoring the camouflage coating emissivity and netting porosity to produce the closet thermal radiance match with the adjacent background scene for a particular set of enviromental and seasonal conditions. Thermal performance of a typical passively matched camouflage system is successful against some backgrounds, some of the time, but not against most backgrounds, most of the time. This illustrates the seemingly insurmountable limitations of the passive approaches to cope with the dynamics of multiple environmental conditions.
It has been attempted to achieve a more substantial thermal concealment improvement by considering some active or semi-active controls of natural of forced convection in conjunction with a semi-transparent camouflage. While active controls provide better performance, the semi-active controls are simpler and sometimes more suitable for lower priority equipment. Both active and semi-active controls for background thermal matching are addressed in this disclosure. The semi-transparent camouflage, characterized by a spectrally-selective transparency, is a common element of both actively and semi-actively controlled embodiments of this invention. The key feature of the spectrally-selective transparency of the camouflage material is that this material has a relatively high solar transmittance coupled with relatively low thermal transmittance.
A key problem with the current used porous net concept is that although it will block some of the thermal energy emitted by a thermally dissipating target, some percentage of this energy will escape directly through the holes in the netting. Although this is acceptable against some hotter backgrounds when considering only area-averaged radiance of the net target combination, it does permit partial direct viewing of the target to be concealed. A non-porous blanket, on the other hand, will completely block the target but would tend to be itself heated due to incident solarl radiation (insolation) and by the target below, without any convective cooling flow.
The principal object of the invention is to provide an infrared camouflage system of simple structure which functions naturally, or with augmented forced flow.
An object of the invention is to provide an infrared camouflage system which functions efficiently and effectively in a natural manner without the need for a power source.
Another object of the invention is to provide an infrared camouflage system which is devoid of blowers, fans, electrical wiring or a source of electrical energy and requires little, if any, maintenance.
Still another object of the invention is to use natural convection cooling for inducing outside airflow through air passages between semi-transparent camouflage and equipment to be protected.
Yet another object of the invention is to augment natural convection, when required, by air fan or other means for providing greater airflow through air passages between camouflage and equipment to be protected.
An object of the invention is to provide semiactive, or manually adjusted, or active (automatically-driven) controls for adjusting inlet and/or outlet openings for airflow.
Another object of the invention is to provide the contrast temperature sensing means in conjunction with active or semiactive controls for achieving a variable airflow and thereby maintaning the contrast temperatures within the background clutter limits.
Still another object of the invention is to provide an infrared camouflage system of simple structure which is inexpensive in cost and requires essentially no maintenance.
Yet another object of the invention is to provide an infrared camouflage system which is set up and removed with speed and facility and functions efficiently, effectively and reliably to protect equipment from IR detection.
An object of the invention is to provide an IR camouflage system which, although it is inexpensive in cost and handled, packed and transported with speed and facility, protects high value military equipment on the ground from IR detection.
Another object of the invention is to provide an IR camouflage system which occupies a very small space when packed for transport and is handled with great facility and speed to cover and uncover high value military equipment on the ground, thereby protecting such equipment from IR detection.
Still another object of the invention is to provide an IR camouflage system which may readily be combined with existing visual and radar concealment systems to achieve a multi-spectral protection with minimal impact on IR, radar and visual concealment.